B. When you want to say "I want to do something." say "Nani ka ga shitai desu."Examples1. Kono kikai ga tsukaitai desu."I want to use this machine."2. Kono kutsu ga kaitai desu."I want to buy this pair of shoes."3. Sakana ga tabetai desu."I want to eat fish."What are common in these three examples above are : 1. all sentences end with desu, so they are polite ; 2. desu follows a word ending in -tai ; and 3. the particle ga precedes a word ending in -tai.

A word ending in -tai comes from a verb base { -tai. The suffix –tai indicates the speaker's and the hearer's desire and changes a verb into an –I adjective.The sentence pattern for "I want to do something." is :

X ga verb base -tai desu.

In this sentence pattern also, ga indicates the direct object, but it sometimes changes to the particle o.Examples1. Nihongo no hon ga/o yomitai desu."I want to read a Japanese book."2. Sakana wa tabetaku arimasen."I don't want to eat fish."3. Kinoo depaato de kaimono ga shitakatta desu."I wanted to do some shopping at a department store yesterday."C. In Japanese culture, it is not good manners to ask one's superior's desire directly.Instead, you should say "X wa doo/ikaga desu ka." As explained in Lesson 3,NOTES ON SENTENCE GRAMMAR IV, ikaga is the polite counterpart of doo, so ikaga is better to use when talking to your superiors.Example A : Sensee, koohii wa ikaga desuka. "Would you like some coffee, professor?" B : Ee, itadakimasu yo. "Yes, please."

C. If you replace kudasai with kudasaimasen ka, you will sound more polite.
Cashing a check, making a cash card, etc. are usual services for a bank to offer. However, teaching how to use a machine is an extra one, so Lwin says, "Kono kikai ga tsukaitai n desu ga, oshiete kudasaimasen ka." "I'd like to use this machine. Would you please tell me how to use it?" in the third line, Dialogue 7-3.

D. When you ask your customer to push the button, "Kono botan o oshite kudasai." is not appropriate, because this sentence sounds a little rude. Instead, you should say :
Kono botan o ooshi kudasai.
This sentence sounds more formal than "Oshite kudasai." or "Oshite kudasaimasen ka." Ooshi in the above sentence is obtained by dropping –masu from oshimasu(the polite form of osu "push") and adding o- to it. When the masu part is taken out of a verb ending in -masu, the remaining part will be called the verb base in this textbook.

Examples
1. Rajio o okiki kudasai.
"Will you listen to the radio?"
2. Motto yukkuri ohanashi kudasai.
"Could you speak more slowly?"
3. Kore o omochi kudasai.
"Will you take this one with you?"
O { verb base { kudasai is often used by clerks, salesmen, etc. in situations such as in a bank, a department store or a ceremony. Note that there are some verbs which don't have o { verb base { kudasai : miru, kuru, suru, etc.